Improved robotic working tool

ABSTRACT

A robotic work tool system ( 200 ) comprising a charging station ( 210 ) and a robotic work tool ( 100 ), said robotic work tool ( 100 ) comprising a position determining device ( 190 ) and a controller ( 210 ), wherein said controller ( 210 ) is configured to determine a current position for the robotic work tool ( 100 ) based on the position determining device ( 190 ), determine a first distance from the current position to said charging station ( 210 ), cause said robotic work tool ( 100 ) to travel a predetermined distance or for a predetermined time, determine a new current position for the robotic work tool ( 100 ) based on the position determining device ( 190 ), determine a second distance from the new current position to said charging station ( 210 ), determine if the second distance is larger than the first distance; and if so, cause the robotic work tool ( 100 ) to turn towards the charging station ( 210 ).

TECHNICAL FIELD

This application relates to a robotic work tool system for improvednavigation, and in particular to a robotic work tool system for improvednavigation to a charging station.

BACKGROUND

Many robotic work tool systems are enabled to allow the robotic worktool to find a charging station by either following the boundaryfollowing a so called F-field. However, if the F-field can not be sensedor if the route in the F-field is blocked, the robotic work tool maywaste time and power trying to find the charging station.

Using positioning devices such as GPS (Global Positioning System) tonavigate for example a robotic lawnmower may lead to that the roboticwork tool navigates incorrectly at times or places where satellitereception is compromised, for example by threes or structures, commonlyfound in for example gardens.

There is thus a need for a robotic work tool system with a robotic worktool that is able to find its way to charging station without wastingtime or power, while relying on traditional navigational methods.

SUMMARY

It is an object of the teachings of this application to overcome theproblems listed above by providing robotic work tool system comprising acharging station and a robotic work tool, said robotic work toolcomprising a position determining device and a controller, wherein saidcontroller is configured to determine a current position for the roboticwork tool based on the position determining device, determine a firstdistance from the current position to said charging station, cause saidrobotic work tool to travel a predetermined distance or for apredetermined time, determine a new current position for the roboticwork tool based on the position determining device, determine a seconddistance from the new current position to said charging station,determine if the second distance is larger than the first distance; andif so, cause the robotic work tool to turn towards the charging station.

In one embodiment the robotic work tool is a robotic lawnmower. In oneembodiment the robotic work tool 100 is a farming equipment. In oneembodiment the robotic work tool 100 is a golf ball collecting tool. Therobotic work tool 100 may also be a vacuum cleaner, a floor cleaner, astreet sweeper, a snow removal tool, a mine clearance robot or any otherrobotic work tool that is required to operate in a work area in amethodical and systematic or position oriented manner.

It is also an object of the teachings of this application to overcomethe problems listed above by providing method for use in a robotic worktool system comprising charging station and a robotic work tool, saidrobotic work tool comprising a position determining device, wherein saidmethod comprises: determining a current position for the robotic worktool based on the position determining device; determining a firstdistance from the current position to said charging station; causingsaid robotic work tool to travel a predetermined distance or for apredetermined time; determining a new current position for the roboticwork tool based on the position determining device; determining a seconddistance from the new current position to said charging station;determining if the second distance is larger than the first distance;and if so, causing the robotic work tool to turn towards the chargingstation.

The inventors of the present invention have realized, after inventiveand insightful reasoning, that a robotic work tool configured to followa boundary wire for as long as possible before leaving to travel to thecharging station and by determining when the distance to the chargingstation is the shortest a virtual F-field is provided which allows therobotic work tool to use tried and reliable navigational methods whilenot wasting time or power looking for the charging station.

Other features and advantages of the disclosed embodiments will appearfrom the following detailed disclosure, from the attached dependentclaims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the [element, device,component, means, step, etc]” are to be interpreted openly as referringto at least one instance of the element, device, component, means, step,etc., unless explicitly stated otherwise. The steps of any methoddisclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in further detail under reference to theaccompanying drawings in which:

FIG. 1 shows a schematic overview of a robotic work tool according toone embodiment of the teachings of this application;

FIG. 2 shows a schematic view of a robotic working tool system accordingto one embodiment of the teachings of this application;

FIG. 3 shows a schematic overview of a robotic work tool systemillustrating a problem with the contemporary use of F-fields for findingthe charging station;

FIG. 4 shows a schematic overview of a robotic work tool systemaccording to the teachings herein for overcoming the problems of theprior art;

FIG. 5 shows an overview of an example robotic work tool system where anobstacle is blocking the closest route from the robotic work tool to thecharging station;

FIG. 6 shows an overview of an example robotic work tool system wherethe robotic work tool has moved away from the obstacle and the obstacleis no longer blocking the route from the robotic work tool to thecharging station; and

FIG. 7 shows a general flowchart for a method for operating a roboticwork tool according to herein.

DETAILED DESCRIPTION

The disclosed embodiments will now be described more fully hereinafterwith reference to the accompanying drawings, in which certainembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided by way of example so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout.

FIG. 1 shows a schematic overview of a robotic work tool 100 having abody 140 and a plurality of wheels 130. In the exemplary embodiment ofFIG. 1 the robotic work tool 100 has 4 wheels 130, two front wheels 130′and the rear wheels 130″. At least some of the wheels 130 are drivablyconnected to at least one electric motor 150. It should be noted thateven if the description herein is focussed on electric motors,combustion engines may alternatively be used possibly in combinationwith an electric motor.

In the example of FIG. 1, the rear wheels 130″ are connected to each anelectric motor 150. This allows for driving the rear wheels 130″independently of one another which, for example, enables steep turning.

The robotic work tool 100 also comprises a controller 110. Thecontroller 110 may be implemented using instructions that enablehardware functionality, for example, by using executable computerprogram instructions in a general-purpose or special-purpose processorthat may be stored on a computer readable storage medium (disk, memoryetc) 120 to be executed by such a processor. The controller 110 isconfigured to read instructions from the memory 120 and execute theseinstructions to control the operation of the robotic work tool 100. Thecontroller 110 may be implemented using any suitable, publicallyavailable processor or Programmable Logic Circuit (PLC). The memory 120may be used for storing various instructions and data, such as a mapapplication M and may be implemented using any commonly known technologyfor computer-readable memories such as ROM, RAM, SRAM, DRAM, FLASH, DDR,SDRAM or some other memory technology.

The robotic work tool 100 further has at least one sensor 170, in theexample of FIG. 1 there are two sensors 170, arranged to detect amagnetic field (not shown). The sensors are connected to the controller110 and the controller 110 is configured to process any signals receivedfrom the sensors 170. The sensor signals may be caused by the magneticfield caused by a control signal being transmitted through a boundarywire (for more details on charging stations, control signals andboundary wires, see the description below with reference to FIG. 2).This enables the controller 110 to determine whether the robotic worktool 100 is inside or outside an area (referenced 205 in FIG. 2)enclosed by a boundary wire (referenced 250 in FIG. 2).

The controller 110 is connected to the motors 150 for controlling thepropulsion of the robotic work tool 100 which enables the robotic worktool 100 to service an enclosed area without leaving the area.

The robotic work tool 100 also comprises a work tool 160, which may be agrass cutting device, such as a rotating blade 160 driven by a cuttermotor 165. The cutter motor 165 is connected to the controller 110 whichenables the controller 110 to control the operation of the cutter motor165. The controller is also configured to determine the load exerted onthe rotating blade, by for example measure the power delivered to thecutter motor 165 or by measuring the axle torque exerted by the rotatingblade. The robotic work tool 100 is, in one embodiment, a roboticlawnmower.

The robotic work tool 100 may also have (at least) one battery 180 forproviding power to the motors 150 and the cutter motor 165. Connected tothe battery 180 are two charging connectors for receiving a chargingcurrent from a charger (referenced 220 in FIG. 2) of the chargingstation (referenced 210 in FIG. 2).

Alternatively, the batteries may be solar charged.

Alternatively, the robotic work tool and/or the cutter may be driven byan engine.

The robotic work tool 100 is also arranged with a position determiningdevice 190, such as a GNSS (Global Navigation Satellite System) device190. In one embodiment the GNSS device is a GPS (Global PositioningService) device 190. The GNSS device 190 is connected to the controller110 for enabling the controller 110 to determine a current position forthe robotic work tool 100 using the GNSS device and to control themovements of the robotic work tool 100 based on the position. Otherexamples of position determining devices 190 include optical (such aslaser) position determining devices, other radio frequency positiondetermining systems, and ultrawideband (UWB) beacons and receivers.

FIG. 2 shows a schematic view of a robotic working tool system 200comprising a charging station 210 and a boundary wire 250 arranged toenclose a working area 205, the working area 205 not necessarily being apart of the robot system 200.

The robotic work tool 100 of FIG. 2 is a robotic work tool 100 such asdisclosed with reference to FIG. 1. A charging station 210 has a charger220 coupled to, in this embodiment, two charging connectors 230. Thecharging connectors 230 are arranged to co-operate with correspondingcharging connectors 185 of the robotic work tool 100 for charging thebattery 180 of the robotic work tool 100.

The charging station 210 also has, or may be coupled to, a signalgenerator 240 for providing a control signal 255 (for more details seeFIG. 3) to be transmitted through the boundary wire 250. As is known inthe art, the current pulses 255 will generate a magnetic field aroundthe boundary wire 250 which the sensors 170 of the robotic work tool 100will detect. As the robotic work tool 100 (or more accurately, thesensor 170) crosses the boundary wire 250 the direction of the magneticfield will change. The robotic work tool 100 will thus be able todetermine that the boundary wire has been crossed.

Optionally, the charging station 210 also has a guide cable 260 forenabling the robot to find the entrance of the charging station 210. Inone embodiment the guide cable 260 is formed by a loop of the boundarywire 250.

In one alternative or additional embodiment the guide wire 260 is usedto generate a magnetic field for enabling the robotic work tool 100 tofind the charging station without following a guide cable 260. Such amagnetic field is commonly referred to as an F-field 270 and the roboticwork tool is configured to navigate to the charging station 210 bynavigating towards an increasing field strength for the F-field 270. TheF-field 270 may have its center at the charging station or at the guidewire 260. In the latter case the F-field 270 can be used to enable therobotic work tool 100 to find the guide cable 260 or the chargingstation 210 more quickly as it can jump the boundary wire as it sensesthe magnetic field from the F-field 270. In one embodiment the magneticfield from the F-field 270 is differentiated from the magnetic field ofthe boundary wire 250 through a difference in the control signal 255being transmitted through the boundary wire 250 and the control signalgenerating the F-field 270.

The robotic work tool 100 may be configured to find the charging station210 using the F-field 270 in different manners. One alternative is thatthe robotic work tool 100 randomly traverses the work area 205 until itfinds the F-field 270. Another alternative is that the robotic work tool100 follows the boundary wire 250 until it finds the F-field 270 andthen shortcuts from the boundary wire 250 to the charging station 210following the F-field 270.

Combinations of these alternatives are of course also possible, and alsotimed or distance-based combinations are possible. For example, arobotic work tool 100 may be configured to randomly search for theF-field 270 for 5 minutes, or spend time trying to find the F-field 270,and if no F-field 270 has been found, then the robotic work tool 100follows the boundary wire 250 until the charging station 210 or theF-field 270 is found.

It should be noted that many other manners of generating the F-fieldalso exist and are known in the field of robotic work tools.

FIG. 3 shows a schematic overview of a robotic work tool system 200,such as the robotic work tool system 200 of FIG. 2, illustrating aproblem with the contemporary use of F-fields 270 for finding thecharging station 210. In the situation depicted in FIG. 3, the roboticwork tool is too far away to sense the F-field 270 and is headed awayfrom the charging station 210. The robotic work tool 100 will have tofollow the boundary wire 250 all around to find the charging station210. Alternatively, the robotic work tool 100 will jump the boundarywire 250 and start searching randomly for the ff270. In any case, therobotic work tool's current heading is taking the robotic work tool 100away from the charging station 210 and runtime is lost trying to find away back to the charging station 210 unnecessarily using the manners ofthe prior art to find the charging station 210.

However, by utilizing a position determining device, such as a GPSdevice 190, in combination with a map application (referenced M inFIG. 1) stored in the memory 120 of the robotic work tool 100 animproved manner of finding the way to the charging station 210 isprovided. FIG. 4 shows a schematic overview of a robotic work toolsystem 200 according to the teachings herein for overcoming the problemsof the prior art utilizing a GPS device 190 in combination with a mapapplication M finding the way to the charging station 210.

The map application M may in its simplest form simply consist ofcoordinates for the charging station 210 or the guide cable 260. In theExample of FIG. 4 the map application M is simply the coordinates (X;Y)for the guide cable 260. Other more advanced maps such as being definedby Autoset 2.5 may also be used as will be discussed further below.

The robotic work tool 100 may be configured to utilize a virtual F-field410 for finding the way to the charging station 210 (possibly via theguide cable 260). The virtual F-field 410 may be defined as an areawithin which there exists an alternative route to the charging station210. The virtual F-field 410 may for example be defined usingcoordinates in the map application M.

To enable a faster localization of the charging station 210, the roboticwork tool 100 is configured to determine a current position of therobotic work tool 100 and to determine whether the robotic work tool 100is within the virtual F-field 410. If so, the robotic work tool 100 isconfigured to determine a (alternative) route to the charging station210, wherein said route does not fully follow the boundary wire 250.

In the example of FIG. 4, the robotic work tool 100 is configured todetermine that it is at a first distance to the charging station 210 orthe guide cable 260 based on the map application M and the currentposition of the robotic work tool 100 (as the guide cable 260 leads tothe charging station 210, there will not be made any difference betweenthe distance to the charging station 210 and the distance to the guidecable 260 and the distance of the guide cable to the charging station210 will be taken to be part of the distance between the robotic worktool 100 and the charging station 210). As the robotic work tool 100moves forward a new current position and a second distance to thecharging station 210 are determined by the robotic work tool 100 and thesecond distance is compared to the first distance. As long as the seconddistance is shorter than the first distance the robotic work tool movesforward and determines a new second distance, wherein the new firstdistance is set to the old second distance and the comparison isrepeated. That the second distance is larger than the first distanceindicates that the robotic work tool 100 is moving towards the chargingstation 210.

When it is determined by the robotic work tool 100 that the seconddistance becomes larger or is the same as the first distance—whichindicates that the robotic work tool 100 is moving a way from thecharging station 210—a current heading of the robotic work tool 100 andan angle A between the current heading of the robotic work tool 100 andthe position of the charging station 210 are determined and the roboticwork tool 100 is caused to turn that angle A and continue moving towardsthe robotic work tool 100. This should enable the robotic work tool 100to find at least the F-field 270 or the guide cable 260 without anyfurther advanced navigational procedures and also without unnecessarilyspending time looking for the charging station 210.

By following the boundary cable 250 a reliable and tested navigationmethod is used as long as necessary, which navigation method is notdependent on clear satellite coverage or other environmental factors.

Alternatively the robotic work tool releases from the boundary wire 250before the route to the charging station 210 is blocked by the obstacle510.

In some embodiments the map application M may be expanded to includecoordinates or boundaries for obstacles, such as a bush, shrubbery,tree, pond or other obstacle, and/or shapes of the work area.

FIG. 5 shows an overview of an example robotic work tool system 200where an obstacle 510 is blocking the closest route from the roboticwork tool 100 to the charging station 210. As the robotic work tool 100would determine that the second distance is larger than the firstdistance the robotic work tool 100 would be prevented from travellingstraight to the charging station 210 as the route is blocked by anobstacle, such as a bush 510. Circum navigating the obstacle 510 maysend the robotic work tool 100 in a direction that is away from thecharging station 210. To prevent this and alleviate any problems causedby obstacles 510, the map application M further comprises coordinates orother information on obstacles 510 and as the robotic work tooldetermines that the second distance is larger than the first distance,the robotic work tool 100 is configured to determine if there is anobstacle 510 blocking the route to the charging station 210. If so, therobotic work tool 100 is configured to continue travel along theboundary wire 250 until the route from the robotic work tool 100 to thecharging station 210 is no longer blocked by an obstacle 510. Anobstacle may be determined to block a route between the robotic worktool 100 and the charging station 210 if coordinates for the obstacle510, which coordinates may define an area of extension for the obstacle510, is between the coordinates for the charging station 210 and thecurrent position of the robotic work tool 100.

The robotic work tool 100 may also or alternatively be configured toproactively determine if an obstacle 510 will block a route between therobotic work tool 100 and the charging station 210 as the robotic worktool 100 continues travelling in its current heading and if so,determine whether to turn towards the charging station 210 even if thesecond distance is smaller than the first distance. Such determinationmay be made based on an extension of the obstacle 510. If it isdetermined that the obstacle 510 will block the route, the robotic worktool 100 is configured to determine a turn point where the route willnot be blocked, but is also close to the point where the second distanceequals the first distance.

FIG. 6 shows an overview of an example robotic work tool system 200where the robotic work tool 100 has moved away from the obstacle 510 andthe obstacle is no longer blocking the route from the robotic work tool100 to the charging station 210. An angle A may then be determined andthe robotic work tool 100 will turn that angle A and travel towards thecharging station 210.

FIG. 7 shows a general flowchart for a method for operating a roboticwork tool 100 according to herein. The method may be stored asinstructions on a computer readable storage medium and as theinstructions are loaded into and executed by a controller, the method isexecuted.

The robotic work tool 100 determines 700 its current position anddetermines 710 that the robotic work tool 100 is within a virtualF-field 410. The robotic work tool 100 then determines 720 a firstdistance to the charging station 210. Thereafter the robotic work tool100 travels 730 along the boundary wire 250 for a predetermined time(such as 0.5, 1, 2, 5 or 10 seconds or continuously) or alternativelyfor a predetermined distance (such as 0.1, 0.2, 0.5, 1, 2 or 5 meters)and then determines 740 a new current position and determines 750 asecond distance to the charging station 210. The robotic work tool 100compares 760 the first distance to the second distance and if the seconddistance is smaller than the first distance, the robotic work tool 100continues to travel along the boundary wire determining a new seconddistance, wherein a new first distance is the old second distance andcompares again. If the second distance is larger than the firstdistance, the robotic work tool determines 770 an angle A from itscurrent heading to the charging station 210 and turns that angle A,travelling towards the charging station 210.

What happens when the first distance equals the second distance maydepend on a number of factors, such as the time travelled along ehboundary wire 250. In one embodiment the robotic work tool 100 isconfigured to determine the angle A and turn and travel towards thecharging station 210. Alternatively, as is indicated b the dashed box inFIG. 7, and as ahs been disclosed in the above, the robotic work tool100 may also be configured to determine if an obstacle 510 is blockingthe route 765 from the robotic work tool 100 to the charging station210, and if so, continue to travel a long the boundary wire 250 untilthe route is no longer blocked.

One benefit of the teachings herein is that tried navigational methodsare used to the fullest without wasting time or energy trying to findthe charging station 210. A navigation system solely or primarilyrelying on for example GPS devices 190, will in some situations sufferfrom bad satellite reception which may cause the robotic work tool 100to navigate incorrectly.

References to ‘computer-readable storage medium’, ‘computer programproduct’, ‘tangibly embodied computer program’ etc. or a ‘controller’,‘computer’, ‘processor’ etc. should be understood to encompass not onlycomputers having different architectures such as single/multi-processorarchitectures and sequential/parallel architectures but also specializedcircuits such as field-programmable gate arrays (FPGA), applicationspecific circuits (ASIC), signal processing devices and other devices.References to computer program, instructions, code etc. should beunderstood to encompass software for a programmable processor orfirmware such as, for example, the programmable content of a hardwaredevice whether instructions for a processor, or configuration settingsfor a fixed-function device, gate array or programmable logic deviceetc.

The invention has mainly been described above with reference to a fewembodiments. However, as is readily appreciated by a person skilled inthe art, other embodiments than the ones disclosed above are equallypossible within the scope of the invention, as defined by the appendedpatent claims.

1. A robotic work tool system comprising a charging station and arobotic work tool, said robotic work tool comprising a positiondetermining device and a controller, wherein said controller isconfigured to: determine a current position for the robotic work toolbased on the position determining device; determine a first distancefrom the current position to said charging station; cause said roboticwork tool to travel a predetermined distance or for a predeterminedtime; determine a new current position for the robotic work tool basedon the position determining device; determine a second distance from thenew current position to said charging station; determine if the seconddistance is larger than the first distance; and if so, cause the roboticwork tool to turn towards the charging station.
 2. The robotic work toolsystem according to claim 1, wherein the controller is furtherconfigured to cause the robotic work tool to turn towards the chargingstation by determining a current heading of the robotic work tool and todetermine an angle between the current heading and the position of thecharging station and cause the robotic work tool to turn the angle. 3.The robotic work tool system according to claim 1, wherein thecontroller is further configured to determine if an obstacle is blockinga route between the robotic work tool and the charging station and if socause said robotic work tool to travel a predetermined distance or for apredetermined time.
 4. The robotic work tool system according to claim1, wherein the controller is further configured to determine thedistance to the charging station based on coordinates of the chargingstation and wherein the coordinates are stored as part of a mapapplication in a memory of said robotic work tool.
 5. The robotic worktool system according to claim 1, wherein if the second distance is notlarger than the first distance, the controller is configured to: causesaid robotic work tool to travel the predetermined distance or for thepredetermined time; determine a new current position for the roboticwork tool based on the position determining device; determine a newsecond distance from the new current position to said charging station,wherein a new first position is set to be the old second distance;determine if the new second distance is larger than the first distance;and if so, cause the robotic work tool to turn towards the chargingstation.
 6. The robotic work tool system according to claim 1, whereinthe robotic work tool is a robotic lawnmower.
 7. The robotic work toolsystem according to claim 1, wherein the position determining device isa global positioning device.
 8. The robotic work tool system accordingto claim 1, wherein the robotic work tool is caused to travel along aboundary wire comprised in the robotic work tool system.
 9. A method foruse in a robotic work tool system robotic work tool system comprising acharging station and a robotic work tool, said robotic work toolcomprising a position determining device, wherein said method comprises:determining a current position for the robotic work tool based on theposition determining device; determining a first distance from thecurrent position to said charging station; causing said robotic worktool to travel a predetermined distance or for a predetermined time;determining a new current position for the robotic work tool based onthe position determining device; determining a second distance from thenew current position to said charging station; determining if the seconddistance is larger than the first distance; and if so, causing therobotic work tool to turn towards the charging station.